A car bomb has exploded in a commercial neighborhood of central Baghdad, killing at least 13 people and injuring dozens of others.

Witnesses say the blast ripped through the Iraqi capital's Tahrir Square Saturday, just as a convoy of sport-utility vehicles was passing. Such vehicles often are used by private security firms operating in Baghdad.

Iraqi authorities and U.S. military officials say several Americans were killed in the attack, which wounded at least 33 people.